7. When we balance a chemical equation by making the number of each kind of atom the same on both sides, what conservation principle are we using?

8. When O₂ is combined with carbon to form CO₂, is the oxygen oxidised or reduced? When chlorine gas is combined with carbon to form CCl₄, is the chlorine oxidised or reduced? When O₂ and Cl₂ are combined to form the gas CL₂O, which diatomic gas is oxidised and which of them is reduced?

9. Write the oxidation numbers for all the atoms in the molecules H₂O, CO₂, CCl₄, and Cl₂O.

10. Strict application of the rules for calculating oxidation numbers,₁as given in Chapter 6, would lead to what values for C and H in methane, CH₄? Then why do we say, as we did in this chapter, that the oxidation numbers of these atoms are effectively zero in methane, in discussing the nature of combustions?

11. What are the oxidation numbers of the atoms in NaBr and ClBr? When these compounds are formed from pure elements, does an actual transfer of electrons occur from one atom to the other? Which atom receives the electron, if transfer occurs? Are both of these compounds ionic salts? If not, what do different oxidation numbers mean for atoms in the compound that is not a salt?